Abstract
Physical and chemical (partial dissolution) techniques have been applied to a suite of young karst bauxite and laterite samples from the southern peninsula of Haiti. The δ 18O values have been obtained for nine mineral species and range from + 1.0‰ for anatase/rutile to +33.4‰ for authigenic quartz. On one hand, results for quartz, calcite, kaolinite, gibbsite and boehmite compare favourably with δ 18O values predicted from accepted mineral-water fractionation factors, assuming modern temperatures (25 ± 2° C) and water δ 18O values ( −3.1 ± 0.5‰). On the other hand, the δ 18O values measured for anatase, illite/smectite, chlorite/smectite, and some iron oxide samples do not compare favourably with predicted values. Departures from expected values for these minerals may be related to crystallization from water with a different δ 18O value than modern water, an imprecise knowledge of some mineralwater fractionation factors under surficial conditions, or nonattainment of isotopic equilibrium between mineral and water during formation. Partial dissolution techniques hold considerable promise for obtaining quantitative δ 18O values of individual minerals in single samples of complex, fine-grained regolith material.
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